Around the same time, in a calf brain, Rabi Simantov and Solomon H. Snyder of the United States found[9] what Eric Simon (who independently discovered opioid receptors in vertebral brains) later termed "endorphin" by an abbreviation of "endogenous morphine", meaning "morphine produced naturally in the body".[3] Studies have demonstrated that human and diverse animal tissues are capable of producing morphine, which is not a peptide.[10][11]

Endorphins are naturally produced in response to pain, but their production can also be triggered by various human activities. Vigorous aerobic exercise can stimulate the release of β-endorphin, a potent μ-opioid receptoragonist, in the human brain, which contributes to a phenomenon known as a "runner's high".[12][13] Laughter may also stimulate endorphin production; a 2011 study showed that attendees at a comedy club showed increased resistance to pain.[14]

Endorphins are suspected to play a role in depersonalization disorder. The opioid antagonistsnaloxone and naltrexone have both been proven to be successful in treating depersonalization.[15][16] Quoting a 2001 study involving the drug naloxone, "in [3] of 14 patients, depersonalization symptoms disappeared entirely, and [7] patients showed a marked improvement. The therapeutic effect of naloxone provides evidence for the role of the endogenous opioid system in the pathogenesis of depersonalization."[15][non-primary source needed]

^Malenka RC, Nestler EJ, Hyman SE (2009). "Chapter 7: Neuropeptides". In Sydor A, Brown RY. Molecular Neuropharmacology: A Foundation for Clinical Neuroscience (2nd ed.). New York: McGraw-Hill Medical. pp. 183, 192. ISBN9780071481274. Different patterns of tissue-specific cleavage is another step by which a diversity of signaling peptides can be generated. Posttranslational processing can be illustrated by the cleavage and modification of proopiomelanocortin (POMC), the precursor of several peptides with distinct biological actions, including adrenocorticotropic hormone (ACTH), α-melanocytestimulating hormone (α-MSH; also called melanocortin), and β-endorphin.